A king tide washes up along the Embarcadero in San Francisco on Jan. 3. Higher-than-average tides are expected again every morning from Thursday through Monday.
Brontë Wittpenn, Staff photographer / Brontë WittpennThe atmospheric rivers may have subsided, but Mother Nature isn’t done flooding California just yet. On Saturday and Sunday, “king tides” of over 7 feet are expected to cause minor coastal flooding along low-lying areas, according to the National Weather Service Bay Area office.
King tides, unlike the brutal downpours in recent weeks, are natural phenomena not related to climate change. But scientists say king tides, high tides that are 1 to 2 feet higher than the average high tide, portend what California’s shoreline will look like as climate change hastens sea level rise in the not-too-distant future.
“The king tides of today are going to be the normal high tides of the future,” said Lori Lambertson, a science educator at the San Francisco Exploratorium.
Ocean tides are caused by the gravitational pull of the moon and the sun. King tides occur when several astronomical events happen at the same time: when there’s a new or full moon, when the moon is closest to the Earth and when the Earth is closest to the sun, Lambertson said.
Higher-than-average tides are expected every morning Thursday through Monday, according to a Tuesday update from the National Weather Service. The tide will peak around 10:15 a.m. Saturday at 7.16 feet, the NWS said.
The most recent king tides occurred Dec. 22 and 23, just a week before atmospheric rivers battered the region.
This weekend’s king tides combined with water flow from recent storms is “probably going to create the highest tide seen in a long time,” particularly in areas where freshwater and ocean water mix, according to Michael Vasey, a lecturer at San Francisco State University’s Estuary & Ocean Science Center. That’s because ocean water is denser than freshwater and acts as “a wedge that lifts that freshwater even higher,” Vasey said.
“If I were the public works officials around the Bay, I would be mobilizing and getting ready,” Vasey said.
King tides also usher in lower low tides in the afternoons: The lowest tide of -1.76 feet is expected Saturday around 5:15 p.m., the NWS said. During low tide, people can go tidepooling and see “a lot more of that underwater life than they usually do,” said Annie Kohut Frankel, manager of the California King Tides Project with the California Coastal Commission.
“If you go to the same place and hang out at the shoreline all day long, you’re gonna see really dramatic changes,” Frankel said.
The King Tides Project is asking people to take and share photos of king tides in their area at tinyurl.com/yzzrxj93 . The website has a map that shows the highest predicted tide at locations along the coastline.
There are also numerous king tide walking events this weekend around the Bay Area and California to learn more about king tides and sea level rise vulnerability, including one hosted by the Exploratorium and the Port of San Francisco on Saturday from 10 to 11 a.m.
The photos “help us better understand the future that we’re looking at as sea levels rise, so we can understand what’s vulnerable,” Frankel said.
Claire Hao is a San Francisco Chronicle staff writer. Email: claire.hao@sfchronicle.com
Twitter: @clairehao_
